Human-derived stem cells such as ES cells and iPS cells have an ability to differentiate into many kinds of cells (pluripotency), and have attracted attention in that they enable large-scale pharmacometrics and medical applications using human cells which have been difficult, such as analysis of diseases, drug discovery screening, toxicity testing, and regenerative medicine. A differentiation efficiency in differentiation induction from these stem cells into desired cells is considered to be largely dependent on the state of the stem cells as starting materials. That is, the efficiency of differentiation induction is lowered, unless the stem cells maintain pluripotency and keep an undifferentiated state. Thus, quality control of the stem cells is extremely important for industrial application of the stem cells, and the stem cells need to be monitored and noninvasively assessed for their states.
In addition, since these stem cells form a confluent cell population (colony) by adhesion (contact) of approximately thousands to tens of thousands of stem cells, quality control is also usually conducted in increments of colonies.
For example, Patent Document 1 discloses a cell analytical method in a cell analyzer for analyzing a cell colony using an optical path length image of a cell colony composed of a large number of cells, which is characterized by comprising an obtention step of obtaining the optical path length image of the cell colony by an obtention means in the cell analyzer, an extraction step of extracting a circular shape corresponding to the cell nucleus of the cell in the obtained optical path length image by an extraction means in the cell analyzer, a comparison step of comparing an inner optical path length with an outer optical path length of the extracted circular shape by the comparison means of the cell analyzer, and an analysis step of analyzing the cell colony by an analysis means in the cell analyzer based on the compared results.
In addition, Non-Patent Document 1 describes that mean optical path lengths in cytoplasm regions in CHO cells, HeLa cells and osteoclast-like (OC) cells which were differentiated cells were smaller than those in their nuclear areas, on the contrary, a mean optical path length in cytoplasm region in each hiPS cell in the colony was larger than that in its nuclear area, and that a ratio (cytoplasm/nucleus) of optical path lengths can be a simple indicator for discriminating between the hiPS cells and other types of differentiated cells.